Field of the Invention
The present invention concerns a method for creating a composite magnetic resonance (MR) raw dataset for an MR apparatus, and a computer designed to create the composite MR raw dataset for the MR apparatus.
Description of the Prior Art
Magnetic resonance tomography (MRT), based on the physical phenomenon of nuclear magnetic resonance, has been known for many years as an imaging modality in medicine. The areas of application of magnetic resonance apparatuses (MR apparatuses) have been enlarged in recent years by faster imaging techniques. One approach for shortening the measurement time is to reduce the amount of MR raw data to be acquired, and the remaining missing raw data are either constructed with suitable algorithms, or the MR image with artifacts reconstructed from the reduced raw data must be corrected. A further option for enlarging the measurement volumes without prolonging the measurement time is the use of parallel imaging, in which a number of reception coils simultaneously receive the signal from the examination object. In this type of imaging, the MR signals are acquired by a coil array, wherein each coil acquires MR signals in this associated reception region independently of the other coils, and the combination of all coil signals is merged into an MR image. Such parallel imaging is based on two approaches. In a first approach the MR images of the individual reception coils, which have a reduced field of view, are reconstructed and the individual images are subsequently merged with knowledge of the individual coil sensitivities. This method carried out in the imaging space (domain) is known by the name “SENSE”. The other possibility is to explicitly compute missing k-space segments or lines before image reconstruction, i.e. before the transformation of the raw data. These types of method are known by the names “SMASH”, “GRAPPA”, and “CAIPIRINHA”.
With all these types of reconstruction, which take place in the image space or in the raw data space, additional MR calibration measurements are necessarily carried out, with which either the missing raw data lines or segments can be reconstructed in the raw data space, or with which the individual coil sensitivities are computed in the image space.
These calibration measurements can either be integrated into the actual imaging, so that in parallel imaging additional regions are acquired in the raw data space, or separate calibration measurements are carried out. Separate calibration measurement can only be used for the computation of GRAPPA coefficients. In GRAPPA reconstruction, an attempt is made, with a linear combination of measured raw data lines of an incomplete dataset, to reconstruct the non-measured raw data, wherein the linear combination is selected so that the raw data lines created during the reference measurement can be reconstructed.
Overall, however, the acquisition of the reference MR measurement lengthens the overall acquisition time.